The present invention relates, in general, to balancing power sources, and more particularly, to equalizing the voltages of battery cells in a series combination.
Battery cell balancing is required in lithium battery technology. As a battery pack of lithium battery cells in a series combination undergoes a number of charging and discharging cycles, a voltage difference is developed among the battery cells because each lithium battery cell has its own distinct charging and discharging characteristics. The voltage difference creates an imbalance condition among the battery cells, which leads to the loss of capacity in the battery pack.
In one approach for avoiding the loss of battery capacity, the battery cells in a battery pack are balanced during a charging process. The voltages of the battery cells in a battery pack are compared with one another when any one battery cell in the battery pack is measured as having a voltage equal to or greater than a predetermined over voltage limit. If all battery cells are at the over voltage limit, the battery cells in the battery pack are considered as being in balance. Otherwise, the battery cell having the highest voltage is discharged for a predetermined time duration. This approach does not allow the use of the battery pack while the battery cell is being balanced because the charging process must discontinue when any one battery cell is at the over voltage limit. Therefore, this approach does not provide for uninterrupted use of the battery pack.
Accordingly, it would be advantageous to have a battery balancing circuit and a method for balancing battery cells in a battery pack while the battery pack is idle, being charged, or being discharged, thereby providing for an uninterrupted use of the battery pack. It would be of further advantage to have a battery balancing circuit that does not drain the battery power while the balancing function is disabled.